1. Field of the Invention
The present invention relates to a dielectric ceramic and, more particularly, to a dielectric ceramic which has a high unloaded Q in a high-frequency range, thereby being suitable as a dielectric appliance for high frequencies.
2. Description of the Prior Art
A dielectric resonator and a dielectric substrate which are used for a signal circuit in a high-frequency range such as microwaves and milli waves are generally required to use a dielectric ceramic which has a high dielectric constant, a high unloaded Q, and a small absolute value of the temperature coefficient of the resonant frequency. For dielectric ceramic of this kind, TiO.sub.2 materials have conventionally been used. For example, BaO-TiO.sub.2 and ZrO.sub.2 -SnO.sub.2 -TiO.sub.2 materials, and recently, Ba(Zn,Ta)O.sub.3 and Ba(Mg,Ta)O.sub.3 materials have been utilized. Dielectric ceramic made of these materials are characterized in that the unloaded Q is 3,000 to 7,000, the dielectric constant is 20 to 40, and the temperature coefficient of the resonant frequency is as small as approximately 0 ppm/.degree.C. at a high frequency of about 10 GHz.
Communication apparatus have recently been adopting increasingly higher frequencies, and a dielectric ceramic having a higher unloaded Q is required in the SHF band used for satellite broadcasting, etc.